The ability to isolate large quantities of recombinant proteins purified to homogeneity is particularly important to the pharmaceutical industry. Recombinant proteins produced for therapeutic applications must be free of antigens and toxins found in the host cell used for protein production. Additionally, the recombinant protein should represent an authentic version of the naturally occurring protein, i.e., a protein having the same primary amino acid sequence as found in the naturally occurring protein.
Proteins encoded by recombinant DNA clones may be expressed and purified using a variety of methods. Recombinant proteins may be expressed in prokaryotic hosts or in eukaryotic hosts, such as yeast or mammalian cell lines. Prokaryotic hosts are more widely used for the expression of recombinant proteins. Prokaryotes, such as Escherichia coli (E. coli), are well characterized, easy to manipulate and grow in inexpensive media. Expression of recombinant proteins in eukaryotic hosts is attractive particularly when the protein must contain post-translational modifications which do not occur in prokaryotic hosts.